Contact assembly for a vacuum interrupter



5, 1967 HIROYUKI SUGAWARA 3,356,818

CONTACT ASSEMBLY FOR A VACUUM INTERRUPTER Filed May 17, 1966 UnitedStates Patent 3,356,818 CONTACT ASSEMBLY FOR A VACUUM INTERRUPTERI-Iiroyuki Sugawara, Hitachi-shi, Japan, assignor to Hitachi, Ltd.,Tokyo-to, Japan Filed May 17, 1966, Ser. No. 550,731 Claims priority,application Japan, May 17, 1965,

9 Claims. (Cl. 200-166) ABSTRACT OF THE DISCLOSURE The presentdisclosure relates to an improved contact structure for a vacuuminterrupter which is based on the concept that a transference of an arccan be accomplished by a self induced magnetic transference force whoseeffect is enhanced by a change in curvature of the contact surfaces, andis especially useful for interruption of large AC currents by aninterrupter of minimum size. The improved contact structure is comprisedby a first electrode having a frusto-conical portion and a centrallylocated projecting end portion, with the frusto-conical portion defininga tapered contact face thereon. The projecting end portion is providedwith a curved face the radius of curvature of which is shorter than thatof the contact face of the frusto-conical portion. The contact structureis further comprised by a second electrode having a funnel-shapedportion and a closed-ended sleeve portion extended from thefunnel-shaped portion at the bottom thereof. The funnel-shaped portiondefines a complementary tapered contact face which coacts with that ofthe frusto-conical portion of the first electrode. The width of thecontact faces is sufficienly large to provide an initial self inducedmagnetic transferring force to an are formed therebetween. Theclosed-ended sleeve portion defines a hollow cavity which opens into thebottom of the funnel-shaped portion and operatingly encloses theprojecting end portion of the first electrode.

This invention relates to an improved contact structure for a vacuuminterrupter which is especially useful for interruption of a large A.C.current by an interrupter of minimum size.

When a large A.C. current is interrupted, the developed arc should betransferred away from the contact face of the contact electrodes andeliminated as far as possible. For this purpose, a conventionalinterrupter is provided means for transferring the arc magnetically.Such magnetic arc transfer means generally are either of theselfmagnetizing type or the magnctizable type. The former utilizes theA.C. current to be interrupted as a source for the magnet means, and thelatter utilizes a separate current source. They are, however, bothcomplex in the structure thereof and further involve many difficultiessuch as, for example, maintaining high vacuum in an evacuated vessel,providing good electrical insulation in vacuum, manufacture of contactelectrodes of a material which give off only a minimum amount ofinterfering gas, obtaining a suflicient mechanical strength for thecontact electrodes, and manufacture within a vacuum bulb.

The present invention is established after many experiments and studiesin dynamic'characteristics of arcs in vacuum.

The object of this invention is to provide a new and improved contactassembly for a vacuum interrupter utilizing a new type of structure forcreating an arc transferring force.

Another object is to provide a new contact assembly having a new shapedcontact electrode.

3,356,818 Patented Dec. 5, 1967 A further object is to provide animproved contact assembly that is especially fit for interruption of alarge A.C. current with an interrupter of minimum size.

Before describing the present invention, the following facts should berecognized as a background of this invention.

Within a range of about 12-13 ka. of A.C. current to be interrupted, thearc eliminating condition should be varied in accordance with the amountof the A.C. current to be interrupted and the contact shape of thecontact electrodes.

In case that a contact face has a circular shape, the following formuladefines a boundary condition whether a small current arc or a largecurrent are is developed:

in which (mm) is the diameter of the circular contact face and I (ka.)is the current.

On the other hand, where a contact face is a round band shape, thecondition is provided as follows:

in which d (mm) is the width of the band face.

In case of either shape, a small current are would be developed if thewidth of the contact face exceeds the critical amount defined inFormulas I and II. Otherwise, a large current are would be developed.Therefore, if a circular shape contact face is more than 25 (mm) indiameter, it would be sufficient to be used for interrupting a currentof 5 ka. with a small current arc.

A small current arc, in general, is defined as'a plurality of unit arcsof amperes each having a column shape of 10* (cm) in diameter. Theyrepel one another and scatter zig-zag on the contact face; however, theyhave a tendency to move toward contact portions which have the shortestdistance between the open contact faces. Moreover, each such contactportion should have enough area so that a small current are may scatterthereon as defined in Formula I or II. V

On the other hand, a large current are is defined to be a column of 7-9(mm.) in diameter. This are would melt contact electrodes at the arcsustaining portions thereof if allowed to continue to exist between twoportions for too great a period of time. Where such melting occurs, itinterferes with the recovery of electric insulation between theseparated contact electrodes, even if a gas evacuated metal is used asthe electrode material, and this results in rendering the interrupterinoperable. Therefore, the arc should be transferred from one faceportion to another on the contact face, not only to cool the contactface portions on which the arc is standing, but also to prevent theelectrode from being melted too much. a

One of the most significant facts on which the present invention reliesis the inventors experimental finding that a large current are may betransferable towards a sharply curved electrode portion, i.e., a portionhaving a short radius of curvature. During experiments of the inventor,the transference of an arc was found to'be much more influenced by thechange ofcurvature of contact surface than by thechange of distancebetween contact electrodes. This transferring force on the arc was foundto be produced by the change in curvature of the contact force and couldbe made to be bigger than the magnetic force of a conventional magneticarc-drive system.

The large current are has a large inertia of transference thereof, sothat it will not move easily at the starting time thereofand will. notstop easily once it is moving.

The large current are transfers linearly, so'that if the path on thesurface along which the arc transfers should be curved, its transferencemight be interfered with. Therefore, the path, along which the arctransfers, should be straight.

In order to make the are move at a desired rate, it may be advisable toprovide a difference in curvatures at different surface portions alongthe arc transferring path so as to tailor the transference forcerequirements.

Now the principle of this invention will be described by referring tothe following detailed description when read in conjunction with theaccompanying drawing, in which the single figure illustrated is asectional view of one embodiment of this invention.

In this figure, 1 and 2 are a pair of physically separable contactelectrodes disposed in an evecuated space and fabricated from a gasevacuated conductive metal. The electrode 1 is formed in a funnel shapehaving a tapered inside face 3, a bottom end portion 7 and an an nulartop end portion 16. From the bottom end portion 7, a cylindrical sleeveportion 9 with a closing end 11 is integrally formed to provide a boreat the bottom of the funnel portion. The annular top end portion 16 isprovided with an annular edge 13. This electrode 1 is connected to anelectric conductor 14 for connection to a source of electric current inthe usual manner.

The other electrode 2 is formed to have a frustoconical portion with atapered face 4 thereon and a projecting end portion 6 at the centerthereof. This electrode 2 is connected to an electric conductor 15. Thetapers of respective faces 3 and 4 are provided to be the same, and therespective electrodes 1 and 2 are arranged to operatingly provide aface-to-face contact by the contact faces 3 and 4.

The widths or heights of the contact faces 3 and 4 are advised to bemore than 12 mm., preferably 15-18 mm. Such widths are required for thefollowing reasons. First, in case of interruption of less than 12-13ka., the are becomes a small current are and requires a sufficientcontact area as defined by the Formula II. Second, in case ofinterruption of a large current, the arc becomes a large current are anda continuous change in curvature of the contact surface for a sufiicientdistance is required for providing an initial self produced magnetictransferring force to the arc to cause the arc to be moved from betweenthe contact surfaces, 3 and 4 toward the projecting end portion 6 andinto the bore 5.

The projecting end portion 6 is extended integrally from the top portionof frustoconical portion of the electrode 2. The top end of theprojecting end portion 6 is shaped to form a spherical surface having aminimum radius of curvature. The projecting end portion 6 may be axiallyelongated. The curvature of the peripheral surface of the projecting endportion 6 is defined by a certain radius of curvature which may belonger than the minimum radius of curvature of the top spherical face 10but shorter than that of the contact face 4.

Both the contact electrodes 1 and 2 are reciprocally moved axially by acontroller, not shown. When the contact faces 3 and 4 are separated tointerrupt AC. current, an arc would be developed therebetween. Where thearc is a small current are, a plurality of unit arc columns aretransferred towards the bore 5 by a magnetic force originated by thecurrent to be interrupted. Where the arc is a large current arc, an arccolumn is centripetally forced to move closer to the projecting endportion 6 By the difference in radius of curvature at contact faceportions as discussed above. Also, as the two contact electrodes 1 and 2separate, the distance between the contact faces 3 and 4 increases whilethe distance between the peripheral surface of projecting end portion 6and the inside surface of bore portion 5 remains the same. This resultsin further forcing the are into bore portion 5. The annular edge portion13 is formed to prevent any evaporated metal from spattering on an outervacuum vessel, not shown.

According to this invention, the arc is caused to be transferred intothe bore portion 5 as the two contacts 1 and 2 physically separate, sothat spattering of evaporated metal is almost entirely included withinthe inside space of bore 5 rather than between the contacting electrodefaces 3 and 4. Hence, proper operation of the interrupter is assured. Asa further consequence, the vacuum vessel in which the contacts aredisposed may be formed in a small size, and this contributes tominimizing the size of the over-all interrupter.

From the foregoing description, it can be appreciated therefore that theinvention makes available a new and improved vacuum interrupter which isespecially useful for interruption of a large A.C. current by aninterrupter of minimum size.

Having described one embodiment of a vacuum interrupter constructed inaccordance with the invention, it is believed obvious that othermodifications and variations of the present invention are possible inthe light of the above teachings. It is therefore to be understood thatchanges may be made in the particular embodiment of the inventiondescribed which are within the full intended scope of the invention asdefined by the appended claims.

I claim:

1. A contact assembly for a vacuum interrupter, comprising:

a first electrode having a frusto-conical portion and a centrallylocated projecting portion, said frusto-conical portion defining atapered contact face thereon, said projecting portion providing a curvedface the radius of curvature of which is shorter than that of saidcontact face of said frusto-conical portion, and

a second electrode havingv a funnel-shaped portion and a closed-endedsleeve portion extended from said funnel-shaped portion at the bottomthereof, said funnel-shaped portion defining a complementary taperedcontact face to that of said frusto-conical portion of said firstelectrode, said frusto-conical portion and said funnel-shaped portionoperatingly contacting one another at the contact faces the width of thecontact faces being sufficiently large to provide an initial selfinduced magnetic transferring force to an arc formed therebetween, andsaid closed-ended sleeve portion defining therein a hollow cavity whichopens into the bottom of said funnel-shaped portion and operatinglyencloses therein said projecting portion of said first electrode theprojecting portion of said first electrode being spaced-apart from thewalls of the enclosing hollow cavity a fixed distance which isrelatively short in comparison to the width of the contact faces.

2. A contact assembly as defined in claim 1, in which said projectingportion is in the form of a cylindrically shaped rod having a certainlength and a spherically shaped end atop thereof, and said sleeveportion is formed in a surrounding cylinder portion closed at one endthereof and integrated to the bottom of said funnel-shaped portion atthe other end thereof, said rod being centrally disposed in saidcylinder and spaced apart therefrom a constant distance during closureof the contact faces of the assembly.

3. A contact assembly as defined in claim 1, in which said funnel-shapedportion further includes an annular edge portion extending from an upperend thereof.

4. A contact assembly as defined in claim 2, in which said funnel-shapedportion further includes an annular edge portion extending from an upperend thereof.

5. A contact assembly as defined in claim 2, in which the peripheralsurface of the projecting end portion has a radius of curvature which islonger than the minimum radius of curvature of the spherically shapedend thereof and is shorter than the radius of curvature of thecomplementary tapered contact faces.

6. A contact assembly as' defined in claim 5 in which said funnel-shapedportion further includes an annular edge portion extending from an upperend thereof.

7. A contact assembly for a vacuum interrupter according to claim 1, inwhich the width of the contact faces is more than 12 mm.

8. A contact assembly for a vacuum interrupter according to claim 1 inwhich the width of the contact faces has a value which is more than 15mm. and less than 18 9. A contact assembly for a vacuum interrupter,comprising:

a first electrode having a frusto-conic'al portion and a centrallylocated projecting portion, said frusto-conical portion defining atapered contact face thereon, and

a second electrode having a funnel-shaped portion and a closed-endedsleeve portion extended from said funnel-shaped portion at the bottomthereof, said funnel-shaped portion defining a complementary taperedcontact face to that of said frusto-conical portion of said firstelectrode, said frusto-conical portion and said funnel-shaped portionoperatingly contacting one another at the contact faces, the width ofthe contact faces being sufiiciently large to provide an initial selfinduced magnetic transferring force to an arc formed therebetween, andsaid closed-ended sleeve portion defining therein a hollow cavity whichopens into the bottom of said funnel-shaped portion and operatin'glyencloses therein said projecting portion of said first electrode.

References Cited UNITED STATES PATENTS ROBERT S. MACON, PrimaryExaminer.

ROBERT K. SCHAEFER, Examiner.

H. O. JONES, Assistant Examiner.

9. A CONTACT ASSEMBLY FOR A VACUUM INTERRUPTER, COMPRISING: A FIRST ELECTRODE HAVING A FRUSTO-CONICAL PORTION AND A CENTRALLY LOCATED PROJECTING PORTION, SAID FRUSTON-CONICAL PORTION DEFINING A TAPERED CONTACT FACE THEREON, AND A SECOND ELECTRODE HAVING A FUNNEL-SHAPED PORTION AND A CLOSED-ENDED SLEEVE PORTION EXTENDED FROM SAID FUNNEL-SHAPED PORTION AT THE BOTTOM THEREOF, SAID FUNNEL-SHAPED PORTION DEFINING A COMPLEMENTARY TAPERED CONTACT FACE TO THAT OF SAID FRUSTO-CONICAL PORTION OF SAID FIRST ELECTRODE, SAID FRUSTO-CONICAL PORTION AND SAID FUNNEL-SHAPED PORTION OPERATINGLY CONTACTING ONE ANOTHER AT THE CONTACT FACES, THE WIDTH OF THE CONTACT FACES BEING SUFFICIENTLY LARGE TO PROVIDE AN INITIAL SELF INDUCED MAGNETIC TRANSFERRING FORCE TO AN ARC FORMED THEREBETWEEN, AND SAID CLOSED-ENDED SLEEVE PORTION DEFINING THEREIN A HOLLOW CAVITY WHICH OPENS INTO THE BOTTOM OF SAID FUNNEL-SHAPED PORTION AND OPERATINGLY ENCLOSES THEREIN SAID PROJECTING PORTION OF SAID FIRST ELECTRODE. 